WASHINGTON – A corporate executive, his wife, their 10-year-old son and a housekeeper were slain inside a multimillion-dollar northwest Washington home that was set on fire, District of Columbia police said Friday while offering no details about who might have killed them or why.

At least three of the victims suffered stab wounds or blunt-force injuries and all four were homicide victims, Police Chief Cathy Lanier said Friday. The injuries were sustained before the fire was set on Thursday afternoon.

Lanier identified the couple as Savvas Savopolous, 46, and his wife, Amy Savopolous, 47. She said the other two victims had been tentatively identified as the couple's 10-year-old son, Philip, and a housekeeper, Veralicia Figurera, 57.

The couple had two older daughters who, according to neighbors, attend boarding schools out of state. The daughters are safe and police know their whereabouts, a police spokeswoman said.

Police were seeking information about a blue 2008 Porsche belonging to the family that was found Thursday night in Prince George's County, Maryland. The car had also been set on fire, Lanier said.

There was no sign of forced entry at the house, and investigators were likely to be there for several more days combing through evidence, Lanier said.

Savvas Savopolous was the president of American Iron Works, a building materials manufacturer based in Hyattsville, Maryland. A person who answered the phone at the company's headquarters declined to comment earlier Friday, and a message left after Savopolous was identified was not immediately returned.

Messages left for relatives of Savopolous were not returned on Friday.

The family home, valued at $4.5 million, is located blocks away from Vice President Joe Biden's official residence and from the Washington National Cathedral, which was preparing to host memorial services for the victims.

The couple's son attended St. Albans School, a private school adjacent to the cathedral.

"Our school community is grieving over this tragic situation at the home of one of our young students," Vance Wilson, headmaster of the school, said in a statement.